On a September day in 1863, Abdul Hamid entered the Central Asian city of Yarkand. Disguised as a merchant, Hamid was in fact an employee of the Survey of India, carrying concealed instruments to enable him to map the geography of the area. Hamid did not live to provide a first-hand account of his travels. But he was the advance guard of an elite group of Indian trans-Himalayan explorers?recruited, trained, and directed by the officers of the Great Trigonometrical Survey of India?who were to traverse much of Tibet and Central Asia during the next thirty years.